Using isolated perfused rabbit lungs, we will determine the immuno-globulin class(es) responsible for inhibition of soluble antigen absorption through the alveolocapillary membrane. This will be accomplished by measuring the rate of antigen absorption through isolated lungs from rabbits passively immunized with a particular purified immunoglobulin class. We will begin to determine the mechanisms whereby antibodies influence the rate of antigen absorption by determining the site of immune complex formation. To determine whether immune complexes form on the air side of the alveolocapillary barrier we will measure the immune complexes in the lavage fluid and bronchoalveolar cells following insufflation with antigen. To determine whether immune complexes form in the blood and then are taken up by the lung from the circulation we will perfuse two isolated lungs in series so that we can measure the absorption of inhaled antigen through the first lung and the uptake of the antigen and/or immune complexes by the second lung, which is perfused with antigen containing blood flowing out of the first lung. We will determine whether pulmonary inflammation and immunization can influence absorption of soluble antigen through the airways of intact rabbits. By comparing the results from the intact rabbits with those from isolated lungs we will be able to evaluate the importance of the mechanisms which influence absorption in the isolated lung to absorption through the airways in the intact animal.